Ceramic treating process and product produced thereby

ABSTRACT

A NEW CERAMIC TREATMENT PROCESS ANDPRODUCT AND, MORE PARTICULARY, A PROCESS FOR TREATING UNDERFIRED POROUS PARTIALLY VITRIFIED RELATIVELY SOFT MACHINABLE REFRACTORY CERAMIC MATERIALS TO PRODUCE HARDENED DIMENSIONALLY STABLE END PRODUCTS AT RELATIVELY LOW TEMPERATURES AND THE CERAMIC MATERIALS PRODUCED THEREBY WHICH ARE SUITABLE FOR APPLICATION AS BEARINGS FOR UNDERSEA SUBMERGENCE, LOW TEMPERATURE BEARINGS FOR ARCTIC VEHICULAR AND MACHINERY APPLICATIONS, PRECISION BEARINGS FOR SPACE USE AND LIQUID METAL LUBRICATED SYSTEMS. THE SOFT CERAMICS CAN BE MACHINED AND SHAPED IN THE SOFT STATE AND HARDENED BY THE PROCESS OF THIS INVENTION AT TEMPERATURES WELL BELOW NORMAL VITRIFICATION TEMPERATURES WITH VIRTUALLY NO CHAGE IN DIMENSIONS FROM THE MACHINED UNTREATED CERAMIC TO THE TREATED AND HARDENED END PRODUCT. OTHER PRODUCTS PRODUCED BY THE PROCESS OF THIS INVENTION PRODUCE ARTICLES HAVING A VERY DENSE SURFACE CAPABLE OF TAKING A HIGH POLISH AND OTHER PRODUCTS HAVE RESULTED IN AN ABRASIVE OR POLISHING STONE HAVING SUPERIOR QUALITIES TO THOSE OF THE ARKANSAS STONES IN RESPECT TO BOTH SPEED OF METAL REMOVAL AND DEGREE OF POLISHING OR SHARPENING. IN ADDITION, COARSER OR FINER GRADES ARE OBTAINABLE COMPARED TO A SINGLE GRADE OF ARKANSAS STONE. OTHER PRODUCTS PRODUCED BY THIS PROCESS HAVE NEGATIVE TEMPERATURES COEFFICIENTS BECOMING VERY GOOD ELECTRICAL AND HEAT CONDUCTORS AT HIGH TEMPERATURES.

United States Patent 3,734,767 CERAMIC TREATING PROCESS AND PRODUCTPRODUCED THEREBY Peter K. Church, Cascade, and Oliver J. Knutson,Colorado Springs, Colo., assiguors to Kaman Sciences Corporation,Colorado Springs, C010.

No Drawing. Continuation of application Ser. No. 642,704, June 1, 1967.This application June 18, 1970, Ser. No. 63,998

Int. Cl. C04b 41/24 US. Cl. 117-123 B 11 Claims ABSTRACT OF THEDISCLOSURE A new ceramic treatment process and product and, moreparticularly, a process for treating underfired porous partiallyvitrified relatively soft machinable refractory ceramic materials toproduce hardened dimensionally stable end products at relatively lowtemperatures and the ceramic materials produced thereby which aresuitable for application as bearings for undersea submergence, lowtemperature bearings for arctic vehicular and machinery applications,precision bearings for space use and liquid metal lubricated systems.The soft ceramics can be machined and shaped in the soft state andhardened by the process of this invention at temperatures well belownormal vitrification temperatures with virtually no change in dimensionsfrom the machined untreated ceramic to the treated and hardened endproduct. Other products produced by the process of this inventionproduce articles having a very dense surface capable of taking a highpolish and other products have resulted in an abrasive or polishingstone having superior qualities to those of the Arkansas stones inrespect to both speed of metal removal and degree of polishing orsharpening. In addition, coarser or finer grades are obtainable comparedto a single grade of Arkansas stone. Other products produced by thisprocess have negative temperature coefficients becoming very goodelectrical and heat conductors at high temperatures.

This application is a continuation of application Ser. No. 642,704,filed June 1, 1967, now abandoned.

In accordance with the present invention, the process of treatingunderfired porous partially vitrified relatively soft refractory ceramiccomprising the steps of shaping an underfired partially vitrifiedrelatively soft refractory ceramic into a predetermined shape,impregnating the shaped ceramic with phosphoric acid and curing theimpregnated ceramic at temperatures of at least 600" F., but belowvitrification temperatures for a time sufficient to drive out themoisture and produce a hard ceramic.

Ceramic materials normally undergo substantial dimensional changesduring the usual firing or vitrification steps. Thus, it has heretoforebeen extremely difiicult to produce precision parts or intricate shapesfrom ceramics. Precision parts had to be shaped slightly oversize beforefiring. After firing the parts required further machining with diamondcutting wheels or by using lapping methods. Many intricate shapes werejust not available since thin sections of parts would crack duringfiring.

In accordance with the present invention, it has been found thatunderfired or so-called machinable grade refractory ceramics can beshaped while in the relatively soft state and then impregnated and heattreated to produce a ceramic having all the characteristics of avitrified ceramic without the usual change in dimensions. The process ofthe instant invention appears to be useful in the treatment of suchrefractory ceramic materials as the oxides of aluminum, beryllium,zirconium, titanium, magnesium and the like. These materials in thecommercially available machinable grade are quite soft and easilybroken. Also, in the soft state, they can be readily cut with carbidecutting tools, drilled, filed, sanded and otherwise formed topractically any desired shape. One such alu minum and beryllium oxidematerial is available from Coors Ceramic Company of Golden, Colorado.When the machinable ceramics are treated by the method of thisinvention, they become very hard, approximating highly vitrified ceramicand, in addition, will retain the original machined and pre-treateddimensions. The treated material becomes so hard that the only practicalmethod to do further machining is with diamond cutting wheels or byusing lapping techniques.

The commercial value of the instant invention is readily seen when it isrecognized that close tolerances on many intricate vitrified ceramicparts can only be obtained by machining with diamond cutting methodsafter firing. This is the case since there is considerable shrinkagewhich occurs during the firing. Also, there are many desired shapeswhich cannot be economically cast or molded during the firing process.In addition, it is often not feasible to construct molding dies forsmall quantities of a particular part. The method of the presentinvention in contrast thereto permits easy machining of parts to exacttolerances and then hardening the part without change in originaldimensions.

It is, therefore, the principal object of this invention to provide animproved process for shaping, treating and hardening of machinableceramics which avoids one or more of the disadvantages of prior artmethods of produce ing close tolerance hardened shaped ceramic parts.

A further object of the present invention is to provide an improvedprocess of producing hardened ceramic articles of manufacture ofpredetermined shapes, of predetermined characteristics and ofpredetermined dimensions.

Another object is to provide an improved method of producing closetolerance ceramic shapes of selected hardness, porosity and surfacecharacteristics.

A still further object of the invention is to provide an improvedprocess for the production of ceramic bearings capable of use with orwithout lubricants in hostile environments.

A further object of the invention is to provide an improved process forthe production of an improved abrasive or polishing stone.

A further object of the invention is to provide a process for theproduction of a refactory ceramic oxide material having a negativetemperature coefiicient of electrical and heat conduction.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription, and its scope will be pointed out in the appended claims.

This invention is directed to a process and product involving a new typeof ceramic material that is formed by chemically impregnating arelatively soft porous, underfired refractory oxidebase material,followed by a low temperature cure. The resulting ceramic structureformed in this manner has been shown to exhibit extreme hardness, a highcompressive strength and a dimensionally stable material over a widetemperature range. In addition, a number of these new ceramic materialsshow an inherently small coefiicient of friction coupled with a very lowwear rate characteristic.

Parts can be economically fabricated of this new material in a widevariety of intricate shapes and sizes. This is most easily accomplishedby machining the relatively soft and porous refractory oxide basematerial to the final dimensions desired using conventional high speedsteel or carbide tooling. The machined pieces are then chemicallytreated and cured at a temperature substantially below that used fornormal ceramic vitrification.

One of the unique features of this chemical treatment and hardeningmethod is that virtually no change will occur in the original dimensionsof the machined part during the hardening process. Therefore, expensivediamond machining of the finished hardened part is eliminated.

These new ceramic materials will withstand repeated water quenching from1000 F. as well as prolonged exposure to temperature extremes of 2000 F.to --300 F. Mohs scale hardness is in excess of 9, normally being aboutequal to that of silicon carbide. Rockwell hardness can be as high asA-85 to A-90, with associated compressive strengths in excess of 125,000p.s.i.

In addition to their use for the manufacture of precision parts, many ofthese ceramics exhibit excellent characteristics for low friction andlow wear rate bearing and seal applications: in particular, journalbearings, thrust bearings and sliding type bearings and seals. When usedin this manner, lubrication may be by means of a wide variety ofconventional and non-conventional lubricants. Among those successfullytested to date include:

tap water, sea water, alcohol, kerosene, polyethylene glycoltrichlorethylene, lubricating oils, silicone fluids and liquid metals.Solid lubricants have been used with good results at temperatures up toabout 2000 F. In addition,

lightly'loaded bearings have been operated for limited periods at highspeed Without lubrication.

Life tests of sleeve-type bearings have been and still are currently inprogress. However, to date wear has been too low to obtain quantitativedata, even after many months time. Rub-shoe type wear rate tests haveconsequently been conducted and have shown exceptionally low wear ratecharacteristics. For example, a ceramic shoe of this invention riding ona ceramic wheel of the same material exhibited many times less wear thana bearing bronze shoe riding against a steel wheel using oil galling,even when running with such poor lubricants as alcohol or water.

A special variation in treatment of this invention has also been foundthat will produce a honing or finishing material that appears to besuperior in several respects to both natural and artifically producedgrinding stones. For

example, one such ceramic will remove metal far more rapidly than willan Arkansas stone, while at the same time producing a finer and morehighly polished finish.

Another ceramic material of this invention displays a wide variation inelectrical and heat conduction with relatively small changes intemperature.

The basic method employed for producing the new ceramic materialsconsists of chemically impregnating a porous, refractory oxide structurefollowed by a low temperature cure. The porous refractory acts as theskeletal framework around which the final ceramic structure is formed.

The simplest chemical hardening method consists of impregnating theporous refractory structure with a solution of phosphoric acid. Thethoroughly impregnated material is then cured in an oven with the finaltemperature reaching at least 600-1000 F. or higher. With a suitablerefractory base material, this simple acid treatment will produce a hardceramic body having numerous uses.

A more dense, harder and structurally stronger ceramic can be formed byimpregnating the porous base material with one or more refractory oxidesprior to the final acid treatment. This may be accomplished byimpregnation of the porous structure with a water soluble metal saltsolution and subsequently converting to the oxide by simply elevatingthe temperature to the required conversion point. Normally, this salt tooxide conversion will take place at a temperature less than about 1000F.

X-ray diffraction tests indicate that these chemical treatment methodsform a new microcrystalline structure or at least a very close bondbetween the added oxides, and/or phosphoric acid and the porousrefractory skeletal structure.

As mentioned previously, the ceramic material is built around a porousrefractory base material that functions as the skeletal structure. Thetypes of such materials that are suitable for use in the presentinvention include various grades of alumina, titania, beryllia magnesia,magnesium silicate and stabilized zirconia. Silica has been tested butdoes not provide satisfactory results. These materials were obtainedfrom the manufacturer in an underfired or machinable form. In thiscondition, these materials were normally found to be soft enough toallow machining by conventional means, and exhibited a relatively higheffective porosity (10% to to allow for subsequent chemical treatment bythe process of this invention. Table I lists the major type designation,manufacturer, hardness, porosity and fabrication method for each of theskeletal refractory materials tested.

TABLE I.--UNDERFIRED, POROUS REFRACTORY BASE MATERIALS Manufacturer'sSintering Effective Mohs type Major Other temp., porosity, hard- Basematerial designation Manufacturer oxide oxides F. percent ness Remarks0.5% SiOz Alumina AHP-99 Coors 99% A1103 C138 2,670 45.7 2-3 Isostaticpressed.

- o g 99% A1203 2,570 42.4 2-3 Extruded.

99% A1203 1,700 0-1 Do. 99% A1203 2, 130 D0. 99% A1203 2, 642 D0. 99%A120 2, 670 Do. 99% A120 2, 642 Cast. 99% A1203 2, 130 D0. 99% A1203 2,570 D0. 99.5 0 A1203 2,570 Extruded Do AP-997-L3 ..d0 99.7 o A120 2,570Cast.

3.75% SiOz 0.9% CaO Do. AP-94-Il -.d0 94% A120; 0.75% MgO 1,700 33 1 2-3Extruded.

0.5% ZrOz 0.1% F9703 3.75% SiOi 0.9% CaO D0 AP-94-12 .d0 94% A120; 0.75Mg() 2,130 33.0 2-3 D0.

0.5% ZIO2 0.1% F8203 3.75% SiOz 0.9% 0:10 Do. AP-94-I2 --d0 94% A; 0.75%MgO 2,130 44. 1 2-3 Isostatle pressed.

0.5% ZrOz 0.1% F040: 10% SiOz 2.75% MgO AP-85-I1 l0.....-, -r 85% A;1.25% CaO 1,700 33.4 2-3 Extruded,

TABLE I-Continued Manufacturers Sintering Effective Mohs ype Mayor Othertemp., porosity, hard- Base material designation Manufacturer oxideoxides F. percent ness Remarks Alumina AlSiMag 614 Am.- Lava Corp.--"96% A120 6-7 Too hard for easy (underfired). machining. Do AlS1Ma 614Am. Lava G0rp-..-- 96% A1203 Ordered green, fired (green 1-2 r 20 min.at

2,(1100 F. Extruded ro Do- .AlSiMag 393. Am. Lava Corp. 90% A1203 4-5Do- AlSiMag 548 .AJIl. Lava Corp---" 99.8% A1103 Beryllia- BP-96- Coors.96% BeO 1-2 Extruded. Ma 187E4. Du-CoCeramics 89% MgO 1-2 Do 187E77. do96% MgO 1-2 Magneslum s1hcate.- AlSiMag 222 Am. Lava Corp MgO.SiO2 2-3Sihca. #3 Porosity-.- Amersil. Inc 99% SiOz 2-3 Hot pressed. Zircoms172H20 Dn-OoCeramies 95% Z: 1-2 Made from ZCA Type F coarse grainzirconia-(Ca0 stabi- S10 Iized).

2 Titania AlSiMag 192 (un- Am. Lava 0orp.---- 98% T10: {MgO 2,000 2-3Ordered greemfired derfired). 02.0 min. at 2,000 F.

burg, Pa.

These materials are fabricated by one or more of several commerciallyused methods such as powder pressing, extrusion, isostatic forming orslip casting. The important factor, however, is that the formed orpressed oxide be only partially sintered since optimum sintering willresult in a dense body with insufiicient porosity to be usable in thechemical treatment method of this invention.

In addition to the alumina, beryllia, magnesia, titania and zirconiamaterials, it is anticipated that many of the other partially sinteredrefractory oxides would make applicable skeletal structures for theimproved ceramic material. Among these would be the oxides of barium,calcium, cerium, chromium, cobalt, gallium, hafnium, lanthanum,manganese, nickel, niobium, tantalum, thorium, tin, uranium, vanadium,yttrium and zinc. Also, many of. the complex-refractory oxides should besuitable base materials. Of the complex-refractories, only the magnesiumsilicate has been tested to date. Other complex-refractories that may besuitable if produced in a porous, partially sintered (underfired) formare aluminum silicate, aluminum titanate, barium aluminate, bariumsilicate, barium zirconate, beryllium aluminate beryllium silicate,beryllium titanate, beryllium zirconate, calcium, chromite, calciumphosphate, calcium silicate, calcium titanate, calcium zirconate, cobaltaluminate, magnesium aluminate, magnesium chromite, magnesium ferrite,magnesium lanthanate, magnesium silicate, magnesium titanate, magnesiumzirconate, magnesium zirconium, silicate, nickel aluminate, potassiumaluminum silicate, strontium aluminate, strontium phosphate, strontiumzirconate, thorium zirconate, zinc, aluminate, zinc zirconium silicateand" zirconium silicate.

The novel process according to the invention is particularly adapted tothe'treating of porous, partially vitrified refractory ceramics such asthe oxides of aluminum, barium, beryllium, calcium, cerium, chromium,cobalt, gallium, hafnium, lanthanum, magnesium, manganese, nickel,niobium, tantalum, thorium, tin, titanium, uranium, vanadium, yttrium,zinc and zirconium and mixtures thereof. The oxides may be substantiallypure or may contain or have small amounts of impurities or additives,such as an oxide of a metal other than that of the body such as copper,iron, chromium, manganese, nickel, titanium, magnesium, cobalt, cadmiumand the like and/or other salts of such metals which ultimately willconvert to oxides at least during the final curingstep'. The process ofthis invention also contemplates the addition of small amounts ofadditives such as a salt of a metal other than that of the body andconvertible to an oxide such as the chlorides and nitrates of aluminum,copper, chromium, cobalt, magnesium, moylbdenum, nicke1, tin andzirconium which NOTE: American Lava Corp-Chattanooga, Tenn.; Amerisil,Inc-Hillside, New Jersey; Coors-Golden, Colorado;Du-CoCeramics--Saxonare added to the ceramic during treatment. Itappears that the higher purity refractory ceramics are preferablev wheremaximum hardness is desired.

The process of this invention comprises usually the forming of theuntreated ceramic into a predetermined shape. It will be understoodthat, while precast machinable stock may be used, it is possible toprecast to intricate shapes and prefire to an underfired conditionbefore the ceramic is subjected to applicants process. The machinableceramic, either stock or custom cast, is usually quite porous. Thesimplest method of chemically hardening the porous, undenfiredrefractory structure is with a single acid treatment. The ceramic isimpregnated with a concentrated phosphoric acid solution, usually outconcentration. The ceramic can be evacuated in a vacuum before immersionin the acid to hatch the impregnation or, as has been found to beparticularly effective, the ceramic can be heated to from about 300 toabout 600 F. and then immersed in the phosphoric acid solution. Theheating causes a vacuum to be produced within the voids of the ceramicand the phosphoric acid will be drawn all through the ceramic uponimmersion. While a considerably longer time is required, the ceramicalso can be just immersed in the acid solution for a length of timesufficient for complete impregnation. Greater uniformity is achieved by.using the vacuum or heating impregnation techniques. When the part isthoroughly impregnated with acid, it is removed from the solution,excess acid on the surface is drained or wiped off.

Next, applicants novel process comprises the controlled heat curing ofthe acid impregnated ceramic. The heating cycle is usually startedaround F. and ends at about at least 900 F. The ceramic pieces arepreferably placed in powdered asbestos, and the like, to minimize shockduring the heating and cooling cycle. The powdered asbestos also servesto absorb moisture driven out of the ceramic as the temperature israised. The temperature is raised during curing at a rate insuificientto caze the surface of the ceramic.

As pointed out, one of the unique features of the method of theinvention is that virtually no dimensional changes occur in the machinedpiece during the hardening process. Therefore, expensive diamond-typemachining of a hardened part is eliminated.

The porperty of physical hardness has been used as the primary means ofdetermining effects of varying the underfied base materials, chemicaltreatment and curing methods. Table II below sets forth the hardnessmeasurements for various materials which have been given a simple acidtreatment.

H3PO4 impregnation Mohs Rockwell Sample N 0. Base material Typedesignation Manufacturer Major oxide percent hardness hardness Remarks21E Alumina. AP-85-I1 Coors-. 85%, A1203 & 8-9 A66.5 22E dn AP-94- 94%,A120 23E dn Al -04 2 94%, A120; 24E do AP-94-12 (isostatic) -.do 94%,A110 E do AP-99L3 -.do 99%, Alz 3 AHP-99 09%, A120 AlSiMag 614(underfired).. Am. Lava Corp.-- 96%, A1 0;

-. AlSiMag 393 Am. Lava Corp.-- 90%, A1 0 Fractured AlSiMag 548 Am. LavaCorp.-. 99.8%, A120 .---do...-

BP-96-Tl Coors 96%, BcO

a-l Magnesia 187E4. Du-Co Ceramics- 89%, MgO

28-13 Magnesium silicate" AlSilNIag 222 Am. Lava Corp--- MgO-SiOz27E-.-- Silica #3 porosity Amersil, Inc 99%, SiO

56T.... Titania... AlSiMag 192 (underfired) Am. Lava Corp..- TiOz Z-lZirr'nni't 172F120 Du-Co Ceramics 95%, ZrOz 44l..-- Alumina--- AlSiMag(2000 F.) Am. Lava Corp..- MgO-Si02 060.... do AP-99C-I2 Coors 99%,A1203 146 do AP-99CL1 --d 99%, A1203 Several significant differences inthe final product are achieved by the variation of portions of thetreating process. While a pure or nearly pure ceramic material can besignificantly hardened by a simple acid treatment, impregnation of theceramic with a solution of a salt convertible to an oxide and convertingsame to the oxide will produce an increase in the hardness of theceramic and the further acid treatment produces an even harder endproduct.

Where the ceramic material is impregnated with 85% or higherconcentration of phosphoric acid and heat treated, a good bearingmaterial is produced and two pieces of this same material will slideagainst one another with a low coefficient of friction. After suchpieces are worn in for a short while, a shiny surface film is producedwhich remains shiny even at elevated temperatures. Where the moreconcentrated phosphoric acid is used, the resulting product is moredense with smaller unfilled pores. Where a relatively pure ceramic oxideis treated, the addition thereto of another oxide during treatmentsubstantially increases the hardness of the finished product. While itis not completely known what occurs in the treating process, the poresof the underfired ceramic are believed to be filled or partially filledwith a reaction product of the ceramic and the additive, if any, withthe acid, probably a complex metal phosphate.

Where the ceramic material is impregnated with 85% or higherconcentration of phosphoric acid having dissolved therein aluminumphosphate crystals until saturated at from 250400 F. and is then heattreated, a material is produced which cannot be polished to more than adull finish, is quite porous and makes an excellent polishing andsharpening stone. This characteristic is also produced where thetreatment with phosphoric acid is carried out with dilute acidsolutions. It is believed that less reaction product is available tofill the pores, providing a more open and abrasive surface. Here again,the addition of another oxide during treatment substantially increasesthe hardness of the final product. The starting porous aluminum oxidegrades have ranged from about to about 60% effective porosity and, whensubjected to a starved acid treatment, remain quite porous which mayaccount for the excellent polishing and sharpening characteristics ofthe thus treated material.

The heat treating of the acid impregnated ceramic should be initiated atabout 150 F. to 350 F. for a short period of time to drive out excessmoisture and then the temperature is raised in steps for a series oftime intervals until the final cure is accomplished at at least 500-600F. and preferably at at least 850-900 F. The ceramic will become quitehard at 500 PI-600 F., but good electrical resistivity is not achieveduntil the ceramic is subjected to a temperature of 850 F. or higher.Temperatures above 1000 F. and as high as 3000 F. have been used withgood success. It is found that,'onee the heat tmeat h b n. car i d toabo 8 0 F'? the tem rature may be increased to well above the normalvitrifying temperatures (e.g. 3000 F.) without producing any shrinkageor change in the original physical dimensions. Further, the hightemperatures do not appear to affect the hardness of the material fromthat of the material heated to 850 F.

While the mechanism of applicants process is not completely understood,it is believed that aluminum phosphate may be formed and deposited inthe crystal lattice structure of the aluminum oxide as well as withinthe voids of the porous ceramic. Further, the phosphates of theimpurities and/or additives may be formed and possibly as part of thelattice structure.

As pointed out above, the ceramic materials which are chemically treatedand hardened according to one embodiment of the present process displaythe unique characteristic of exhibiting a low coefficient of frictionwhen sliding against themselves. The coefiicient of friction betweenidentical pieces of the material is considerably less than when used incontact with any dissimilar ceramic or metal tested to date. I

Although these materials may be operated dry where they are lightlyloaded for limited periods of time, the starting friction isconsiderably higher than when a lubricating material is present.Lubrication may be by a number of different liquids such as tap water,sea water, kerosene, trichlorethylene, lubricating oils,'silicone fluidsand liquid metals. Dry lubricants such as molybdenum disulfide, graphiteand the like are also suitable. It is possible also to form thelubricant in situ Within the pore structure of the hearing.

The bearings can be easily and economically fabricated in a wide varietyof shapes and sizes. The untreated ceramic material in the form ofpartially fired bars or plates is machined to size and shape usingconventional high speed steel or carbide tooling. The machined piecesare then chemically treated and hardened at temperatures substantiallybelow normal vitrification temperatures. The hardening occurs withsubstantially no change in dimensions, thus avoiding expensive diamondmachining of the finished part.

The ceramic bearing being fairly porous may be used as the lubricantreservoir analogous to that of sintered bronze bearings. In otherinstances, the bearing can be operated partially or totally submerged inthe lubricant or the non-rotating member can be connected to an externallubricant reservoir. I

Typical bearings fabricated of ceramic according to the presentinvention can withstand repeated water quenching from at least 1000 F.,as well as prolonged exposure to temperatures as high as 2000 F. and aslow as--300 F. The compressive strength is on the order of about 125,000p.s.i. or better, and the hardness on the Mohs scale is between 9-10-oron the order of about A-A.90 o h R k e l sca e.

The ceramic materials of Table I were subjected to several slightlydifferent treatments according to this invention, which are: (1)impregnation in phosphoric acid alone; (2) one or more oxideimpregnations followed by a single phosphoric acid treatment; or (3) oneor more oxide impregnations alone.

A typical acid impregnation process according to the present inventioncomprises heating the ceramic piece to about 300-600 F. for about 20minutes, the piece is then immersed in an 85% phosphoric acid solutionwhile hot for about 40 minutes. The piece is then placed in an oven andprogressively heated from 150 F. to about 1000 F. over a period of about120 minutes. The piece is then cooled to room temperature.

A typical combination salt and acid impregnation process comprisesheating the ceramic piece to about 250- 450 F. for about 20 minutes. Theheated piece is then immersed in the salt solution for about 40 minutes.The piece is removed from the salt solution and cured progressively from150 F. to 1000 F. over a period of 120 minutes. The previous step can berepeated if desired. The piece is then cooled to about 600 F. andimmersed in an 85% phosphoric acid solution for about 40 minutes. Thepiece is then placed in an oven and cured over a temperature range offrom 150 F. to 1000 F. over a period of about 120 minutes andsubsequently cooled to ambient temperature in about 15 minutes.

Fully hardened samples were prepared according to the above treatmentsfrom the materials of Table I.

As previously stated, impurities existing in the base ma terial appearto have an effect on the resultant hardness of the treated piece.Therefore, it was decided to artificially add refractory oxides to theporous base structure prior to treating with the acid. This wasaccomplished by impregnating the refractory base material with anitrate, chloride, acetate or other highly water soluble salt of theoxide desired, and then converting the salt to the metal oxide byheating slowly to an elevated temperature. Following the oxideimpregnation (which may consist of one or more salt treatments), thebody was then treated with phosphoric acid in the same way as in theacid treatment alone.

Tables III, IV, V and VI show the effect of added oxides to Coorsalumina products AHP-99, AP-99-L3, AP-94- I1 and AP-85-Il, respectively.In these tests, three impregnations of the saturated salt were used (toassure ample loading with the desired oxide), followed by the 85phosphoric acid treatment.

It is interesting to note that these tables show a wide variation inhardness depending on the oxide treatment. In some cases, the hardnessis considerably increased over that of the same base material treatedwith acid only, while in others, the increase is not so marked. Thehardness that is obtained with the acid treatment only (no used with the99%, 94% and A1 0 base structures, the resulting ceramic isexceptionally high in hardness as compared to all other oxideimpregnations tested. These four tables also show that the AHP-99material (99% A1 0 is the poorest choice for the base structure of thesefour types. However, since the AP-99-L3 is also a 99% aluminacomposition, it must be assumed that the hardness is not a factor of therefractory purity alone, but that other factors such as difference ineffective pore size is probably responsible for some or all of the noteddifferences.

Tables VII, VIII and IX show the same type of data using aluminum oxidessecured from the American Lava Corporation as their types 393, 548 andunderfired 614. These are 99.8% and 96% A1 0 compositions, respectively.The letters N.M. after Rockwell A, indicates not measured.

Hardness measurements obtained with Coors 96% beryllium oxide for fourdifferent salt impregnations is shown in Table X. It is interesting thatthis base material produces results about equal to the best aluminamaterial tested (Coors AP-99), indicating that refractory skeletalstructures other than alumina are definite candidates for the ceramicfabrication method.

Tables XI and XII show hardness results for oxide impregnated magnesiamaterial. While the hardness values are quite low as compared to thealumina or the bellyllia, that is to be expected since magnesia, even inits fully fired state is not a particularly hard material (Mohs 5 /2Tables XIII and XIV cover AlSiMag #222 magnesium silicate and Amersil99% silica, respectively. For reasons not fully understood, refractorybase materials containing a high percentage of silica do not appear torespond well to the chemical hardening method. Even in these two tests,however, the chromic oxide impregnation provided noticeably betterresults than the other impregnations used.

Table XV lists results obtained with a partially sintered, zirconiarefractory base material. This particular underfired zirconia wasfabricated from a calcia stabilized but coarse grain material. It isanticipated that a fine grined zirconia, and possibly a magnesium oxidestabilized type, would provide better results. Nevertheless, thezirconia also reacts to the chemical hardening method in the samegeneral manner as does the alumina, magnesia and berryllia, and, to alesser extent, the magnesia silicate and silica materials. Table XVAlists results obtained with aluminum oxide material and Table XVB listsresults obtained with titanium dioxide material.

With regard to the effect of pore size, it would be noted that theAHP-99- Coors material has quite large pores, compared to the otherCoors material, being on the order of less than one micron compared with2 to 3 microns for the AHP-99 materials. It would appear that the poresize would preferably be less than 2 microns and substantially uniformin size.

TABLE III.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNA'IIONS USINGCOORS AP9411 ALUMINA REFRACTORY BASE MATERIAL [Acid Treated HardnessMohs 8-9, Rockwell 70.7]

N0. H PO4 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks RemarksAl(NOs)2 3X 85 9-10 A-71.5 None BeClz 3X 85 9-10 A74-..4 d0 Ga(N03)z 3X85 8-9 A-55 do Cd(NOa)2 3X 85 8-9 11-63 Co(NO3)z 3X 85 9-l0 A7l.l do-.

0(NO 3X 85 89 A74.8 r03 3X 85 9-10 A-8L5 011(NO 3X 85 9-10 A-GLO FeOla3X 85 89 A72.5 La(NO:4)2 3X 85 8-9 A53.5 LiG2HaO2 3X 85 8-9 A482 Yes MgMg(CzHaO2)2 3X 85 9-10 Fractured.-- Yes MgCl204 MgCrO4 3X 85 9-10 A 1ONi(NOs): 3X 85 9-10 A75.6

SnCl: 3X 85 9-I0 A-71.7 0..-" Sr(N0a)z 3X 85 89 Fractured..- Yes..-..

TABLE III-Contlnued No. HaPOl salt impregimpregnation, Mohs RockwellSample No. Oxide formed Salt impregnation nations percent hardnesshardness Cracks Remarks Th(NO 3X 85 9-10 A73.5 None...- 2( 2O4)a 3X 859-10 A73.5 HrSiWrgOlo 3X 85 9-10 A-72.1 ZnClz 3X 85 8-9 A-73.8 ZrOClz 3X85 9-10 A-76.1 L-A Firms-C1103 (1)F6C13+(1)Cl03 3X 85 9-10 A-77 TABLEIV.-IIARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGINATIONS USING COORSAP-Sli-llf ALUMINA REFRACTO RY BASE MATE RIA [Acid Treated Hardness Mohs8-9, Rockwell A-55.9]

No. 11 120 salt impregimpregnation, Mohs Rockwell Sample No. Oxideformed Salt impregnation nations percent hardness hardness CracksRemarks A1(NO3)2 3X 85 8-9 A-71 None.. Ce(NO3)a 8X 85 9-10 A-74 Yes---CrO; 3X 85 9-10 A-81 None 8( 2Ha0z)r 3X 85 8-9 A-fiG Ycs Shatteredduring Rockwell test. v Ti(C1O4) 3X 85 8-9 A-68 Yes--- Do. ZrOClg 3X 859-10 A-72 None...

TABLE V.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONS USINGCOORS AP-99-L8 ALUMINA REFRACTORY BASE MATERIAL [Acid Treated HardnessMohs 8-9, Rockwell A-70.5]

No. B 1204 salt impregimpregnation, Mohs Rockwell Sample No. Oxideformed Salt impregnation nations percent hardness hardness CracksRemarks Ce(NO3)z 3X 85 8-9 A-69.1 Yes- Explodedin oven. CrO; 3X 85 9-10A-80.5 Nene MgCrO4 3X 85 9-10 A-71.0 ..do ZrOClz 3X 85 9-10 A60.1 .do...

TABLE VI.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONS USINGCOORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL [Acid Treated HardnessMohs 5-6, Rockwell A-54 L8l No. H 120; salt impregimpregnation, MohsRockwell Sample No. Oxide formed Salt impregnation nations percenthardness hardness Cracks Remarks A1(NO3)2 3X 85 8-9 A-fi0.0 None BeClq3X 85 8-9 A-57.0 Bc(NOa)z 3X 85 6-7 A-67.9 C3(NO3)2 3X 85 6-7 FracturedCd(NOa)r 3X 85 4-5 A-55.0 Ce(NO:)2 3X 85 8-9 A54.9 C0(NO3)2 3X 85 6-7A-62.2 CrOa 3X 85 9-10 A-692 Cu(N03)2 3X 85 4-5 A-471 e 13 3X 85 8-9A-452 La(NOa)a 3X 85 p 8-9 A-590 1110211302 3X 85 5-5 A-531 Mg(C2HaO2)z3X 85 6-7 A-523 MgCrO4 3X 85 9-10 A-63 5 Ni(NO3)2 3X 85 7-8 A-596Pb(NOa)2 3X 85 5-6 A-551 SbCl; 3X 85 6-7 A-59.4 Sl'lClz 3X 85 8-9 A-52.0i ;do..... Sr(MO3)z 3X: 85 8-9 A-26.0 .do.--.- Th(NO3)4 3X 85 9-10A-58.7 2(C2O4)s 3X 85 8-9 A-53.3 HrSiWraOlu 3X 85 8-9 A-BLO Z11(NO3)2 3X85 8-9 A-481 ZnOlz 3X 85 8-9 A-72.8 ZIOCI: 3X 85 8-9 A-61.7

TABLE VIII-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USINGALSIMAG 614 (UNDERFIRED) ALUMINA REFRACTORY BASE MATERIAL [Acid TreatedHardness Mohs 8-9, Rockwell A73.3]

salt impregimpregnation, Mohs Rockwell Oxide formed Salt impregnationnations percent hardness hardness Cracks Remarks CeOa Ce(NOa)z 3X 85 8-9A-69.0 None..- Fractured during Rockwell test.

CrzOa CrO; 3X 85 A-76.0 de Cr Oa ClOs 3X 85 9-10 A-76.0 C00 C0(N0a)2 3X85 9-10 A-73.0 MgCrzOr MgCrO4 3X 85 9-10 A-55.5 M0 Ni(NO )1 3X 85' 6-7A-72.5 ZnO Zn(NO.1)n 3X 85 6-7 A-73.3;- ZrO ZrOCh 3X 85 Y l Fired at2,000 F.

TABLE VIII.-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONS USINGALSHVIAG 393 ALUMINA REFRACTORY BASE MATERIAL [Acid Treated HardnessMohs 8-9, Rockwell A-N.M.]

N o. impregsalt nation,

impregpercent Mohs Rockwell Sample No; Oxide formed Salt impregnationnations P hardness hardness Cracks Remarks CrOa 3X 85 9-10 A-77.0None-.. MgCrO4 3X 85 9-10 Shattered do ZrO Ch 3X 85 8-9 A68.5 do

TABLE IX.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USINGALSIMAG 548 ALUMINA REFRACTORY BASE MATERIAL [Acid Treated Hadness Mohs6-7; Rockwell AN.M.]

No. H=P04 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks Remarks A101- 0 CrO; 3X 85 8-9 Fractured.-- None... MgCnOr MgCrO4 3X 85 8-9 do-.do ZrO; ZrO Cl: 3X 85 8-9 A-76A "do.

ERYLLIA REFRACTORY BASE MATERIAL [Acid Treated Hardness Mohs 6-7,Rockwell A-N.M.]

TABLE X.HARDNESS MEASUBREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USINGCOORS BP-96-11 salt impregimpregnation, Mohs Rockwell Sample No. Oxideformed Salt impregnation nations percent hardness hardness CracksRemarks B-l A1103 Al(N0.-,)a 3X 85 8-9 A-74 None 13-2... Cr O; CrO; 3X85 9-10 A-81 do Shattered in V Rockwell testing.

B-4 MgCrO4 MgCrO4 3X 85 9-10 A-7l do B-3 ZrO ZrO C12 3X 85 9-10 A-75 .doDo.

TABLE XI.--HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USINGDU-CO 89% MAGNESIA REFRACTORY BASE MATERIAL [Acid Treated Hardness Mohs4-5, Rockwell-Fractured] No. H3PO4 salt impregimpregnation, MohsRockwell Sample No. Oxide formed Salt impregnation nations percenthardness hardness Cracks Remarks Al(NO 3X 1 85 4-5 Fractured None- CrOa3X 85 8-9 do .do MgCrO4 3X 85 8-9 A51.5 d0-...- Ti1(C;O4) 3X 85 N.M.N.M. MgO base disintegrated. ZrOU; 3X 85 N.M. N.M. Do.

TABLE XIL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNA'IIONS USINGDU-CO 96% MAGNESIA REFRACTORY BASE MATERIAL [Acid Treated Hardness Mohs4-5, Rockwell A-37 .0]

N0. HQPOA salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks Remarks 6-4A1203 A1(N0a)a 3X 85 3-4 Fractured.-- None 6-2-. CH0; CrOa 3X 85 6-7 do.-do...-- 6-3.. MgCraO4 MgCrOr 3X 85 6-7 A-44.25 6-6, TiO, Tiz(Ca04)s 3X85 N.M. N.M. 6-5 ZrOz ZrOCla 3X 85 NM. N.M

TABLE XIIL-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USINGALSIMAG 222 MAGNESIUM;SILICATE REFRACTORY BASE MATERIAL [Acid TreatedHardness Mohs 2-3, Rockwell AN.M.]

No. HZPO] salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks Remarks AI(NO3X 85 3-4 Fractured None CrOz 3X 85 8-9 d0... "d0"... MS-3 MgCrzOrMgCrO4 3X 85 7-8 A-41 ..do.. Shattered during Rockwell test. MS-4 ZrOzZrOCla 3X 85 1-2 Fractured .-do :r..-

TABLE XIV.-HA'R DNESS MEASUREMENTS FOR VARIOUS OXIDE IMPRE GNATIONSUSING AMERSIL #3., I N POROSITY SILICA REFRACTORY BASE MATERIAL 5 [AcidTreated Hardness Mohs N.M., Rockwell AN.M.]

No. HzPO4 salt impregimpregnation, -Mohs Rockwell Sample No. Oxideformed Salt impregnation nations percent hardness hardness CracksRemarks Oa)7 3X 85 V Ce(NO3): 3X 85 CrOa 3X 85 Mg(CrHr)z 3X 85 MgCrOr 3X85 d A g ZrOCh 3X 85 TABLE XV.HARDNESS MEASUREMENTS roa vARroUs ems iMmE'm q'iereaslfism'a'webits OONIA REFRACTORY BASE 'MATERIA [Acid TreatedHardness Mohs 8-9, .RockwcllA 54;.o] I I g N0. H31 0; saltimprcgimpregnation, Mohs Rockwell 1 Sample No. Oxide formed Saltimpregnation .nations percent hardness hardness Cracksj' RemarksAl(NOa)r 3X- 85 6-7 A-46.8 None CIO: 3X 85 9-10 A66.2 do gwa sOzh 3X 856-1 Frac ured do- MgCrOr 3X 85 9-10 A-58.0 Th(NO3)2 3X 85 6-7 A-53.3Z11(N03)2 3X 85 67 A-44.7 ZrOClg 3X 85 8-9 lk-60.3

TABLE XVA.HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATI O NS U SINGALSIMAG ,4

614 96 A1203 REFRACTORY BASE MATERIAL PARTIALLY SINTERED AT 2,000 F.

[Acid Treated Hardness Mohs 8-9, RockwellA-73.7]

N0. HaPO4 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSaltimpregnation nations percent hardness hardness Cracks Remarks CrOa3X 85 9-10 A82.5 None.. ZrOClz 3X 85 9-10 A-74.5 MgCrOr 3X 85 9- 10 7A4375 Ni(NO3)a 3X 85 9-10 A-69.5

one 85 5-6 A65.5

TABLE XVB.-HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNA'IIONS USINGALSIMAG 192 TITANIA 98 TiOz REFRACTORY BASE MATERIAL PARTIALLY SINTEREDAT 2.000 F.

[Acid Treated Hardness Mohs 4-5, Rockwell AN.M.]

No. H P0 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks Remarks r OrO3X 85 8-9 A-77.5 None ZrOClz 3X' 85 8-9 A-66.0 --.do-. Be(NOa)a 3X 856-7 A69.0 0. Mg(CgH Oz)z 3X 85 Fractured. AKNOz): 3X 85 d MgCrOr 3X 85Non 85 Fractured tested in this manner were selected from the materialsof Table I.

Table XVI shows the effect of 1 through 11 chromic oxide impregnationsusing Coors AP-99-L3 alumina base 65 TABLE xvI.-HARoNEs'svARrAT1 oNwr'rn ii'UMBER 0F oHRoi/nd OXIDE rMr'REoNATioNs name 7' COORS AP-99-L3ALUMINA REFRACTORY BASE MATERIAL material, while Table XIVIA shows theeffect of 1 through 8 ehr'ornicoxide impregnations with AP-94-11 alumina,base material afia"rauaxvrrsnawn"thraiigir '5 ir'n' pregnations withAP-94-12 material. These tables show Itheidefinite'lihcrease in hardnesswith increase in numbers of oxide impregnations. The rate of increase inhardness is also seen to decrease as the :number of liinpregnationsincrease. This would appear to "follow since there is probably less andless interstitial space for the oxides with each successive'treatment.'"Specific gravity and'porosity tests bear this out.

No. f; HaPOlsalt impreg-- impregnation, Mohs Rockwell Sample No.v Oxideformed Salt impregnationnations percent hardness; hardness 1 CH0; CrO 1X9-10 A73.2 Orzo; Grog 3X 85" 9-10 A-SOA. 0x20; CrO; 5X 85 9-10 A83'.9CH0; CrO; 7X 85 9-10 A-87.6 01-203 7 C10; 9X 9-10 A-88.3 o e, is 0:0 asMariana-38.9 A. o.....;

TABLE XVI-A.HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDEIMPREGNATIONS USING COORS AP9411 ALUMINA REFRACTORY BASE-MATERIAL N0.H3PO4 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks Remarks ClOa1x 85 9-10 A-76.4 None-.- grga A80.7 do

I 3 CrOa 4X 85 9-10 i CF03 5X 85 9-10 A-85.0 .d0.-.- CrOa 6X 85 9-10A85.0 d0 CrOa 7X 85 9-10 A-86.0 o--;.e. CrOa 8X 85 9-10 A-87.0 0-...

These tables'show that there is very little difference in the hardnessresults obtained between the AP-49-11 and the AP-94-12 materials. Thedifference between these two base materials is in their sinteringtemperatures, respectively 1700 F. and 2130" F.

Table XVIII shows the results obtained with chromic oxide impregnationson Coors AHP-99 alumina material. While the hardness increases with thenumber of chromic oxide impregnations, the hardness numbers obtained forTABLE XVII.--HARDNESS VARIATION WITH NUMBER OF OXIDE IMPREGNATIONS USINGCOORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL N0. H3PO4 salt impregvimpregnation, Mohs Rockwell Sample No. Oxide formed Salt impregnationnations percent hardness hardness Cracks Remarks L-7 Ono; CrO 1x 9-10A-76.8

CrzOa CrOs 2X 85 9-10 A-79.6 C CrOz 3X 85 9-10 A-81.5 L-5 Cr Og CrOa 4X85 9-10 A-83.9

z-s Orzo: CrO; 9-10 A86.0

CrgO; CrOa 7X 85 9-10 A-83.0 OnO CrOa 9X 85 9-10 A-84.0 6' Or o; CrO;11X 85 9-10 A-85.0

TAB LE XVIIIr-HARDgES S VARIATION WITH NUMBER OF CHROMIO OXIDEIMPREGNATIONS USING ORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL No.HaPO: salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSaltimpregnation nations percent hardness hardness Cracks Remarks CrOg1x 85 Grog 2X 85 8-9 A-57A None... 010 3X 85 9-10 A-69.2 do---- CrOa 4X85 7 8-9 A68.Z do....' 0103 85 9-10 A-73.0 -...do.

oror 85 9-10 A80.0 .do. CrOa 85 9-10 A-76.0 'do-...' CrO 85 9-10 A-79.0

TABLE XIXr-HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDEIMPREGNATIONS USING COORS AP-Q-l2 ALUMINA REFRACTORY BASE MATERIAL saltimpregimpregnation, Mobs Rockwell Sample No. Oxide formed Saltimpregnation nations percent hardness hardness Cracks Remarks Y-l ZrOgzroon 1x 85 8-9 A-71.9 No e"- K-fi ZIOz ZrOClz 2X 85 8-9 A-74.6 do'..5-1 ZrOa zroon as 9-10 A-70.0 do 6-T...; zroi zrooll 85 9-10 A73.0mam-.- 7-1 Z1Oz' zroon s5 9-10 A-73.0 '.-..do. 8-1 ZrO zroon 85 9-10A-80.5 do--.- 9-1 Z1O2 ZI'OCIQ 11X 85 9-10 A-78.0 do

TABLE XX.HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDE IIEIIPREGNATIONS USING C ORS AI-IP-99 ALUMINA'REFRAOTORY BASE MATERIA NO. HPO4 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formed Saltimpregnation nations percent hardness hardness Cracks Remarks zrocn 1x85 5-6 A55.5 None ZrOOlz, 2X 85 9-10 A63.5 d0..... ZrOCls 3X 85 9-10A61.7 ZIOQlz 4X 85 9-10 A71.6 -d0..-..

Tables XIX and XX show the eifect on hardness for 1 throughimpregnations of zirconium oxide into base materials of AP-94-12 andA'HP-99 alumina respectively. Again, the AP-94 material produces greaterhardness than the AHP-99 for comparable impregnations. Also, while theAP-94 material impregnated with zirconium oxide does not produce as hardan end product as does the described except that the impregnant wasmagnesium chromate instead of zirconyl chloride. I

Tables XXII I and XXIV are for eerie oxide impregnated AP-94-11 andAl-lP-99 base material, respectively. Table XXV covers the AP-94material with cobalt nitrate used as the impregnant. Table XXVI is forthe same base material but using a concentrated silico-tungstic acidsolu- TABLE XXL-HARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITEIMPREGNATIONS USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL N0.HaPO; salt impregg impregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks RemarksMgCnOr MgCr04 1X 85 9-10 A-66 MgCnO4 MgCrO4 3X 85 9-10 A-72 MgCraOiMgCrO4 5X 85 9-10 A- TABLE XXIL-HARDNESS VARIATION WITH NUMBER OFMAGNESIUM CHROMITE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORYBASE MATERIAL N0. H3PO4 salt impreg- I impregnation, Mohs Rockwell Oxideformed Salt impregnation nations percent hardness hardness CracksRemarks M-4 MgCIzO4 MgCIOa 1X 6-7 A-50 MgCr Oi MgCrO4 3X 85 9-10 A-53M-G MgCl'aO; MgCrO4 5X 85 9-10 A-6l chromic oxide impregnation, thereverse is true when considering the AHP-99 material. Again, theexplanation is undoubtedly connected with differences in pore size and/30 or impurities in the base material.

Tables XXI and XXII show similar tests to those just TABLEXXIIL-HARDNESS VARIATIONS WITH NUMBER OF CERIC OXIDE IMPREGNATIONS USINGCOORS AP-94-11 ALUMINA REFRACTORY BASE MATERIAL No. HgPO; saltimpregimpregnation, Mohs Rockwell Sample No. Oxide formed Salt.impregnation nations percent hardness hardness Cracks Remarks 0-0 C802Ce(NO3)1 2X 85 8-9 A68.3 'None;.'.;

.. C: Ce(N0a)2 3X 85 9-10 A-71.1 .do....- CeOz Ce(NOa)z 4x 85 0-10 A72.9do..... C803 Ce(NO 5X 85 9-10 A-74.6 .do....- CeO e(NO )g 6X 85 9-10A75.7 do....-

TABLE XXIV.HARDNESS VARIATIONS WITH NUMBER OF CERIC OXIDE IMPREGNATIONSUSING COORS AHP-QS) ALUMINA REFRACTORY BASE MATERIAL No. HaPOl saltimpregimpregnation, Mohs Rockwell Sample No. Oxide formedSaltlmpregnation nations percent hardness hardness Cracks RemarksCe(NOs)z- 3X 85- -8-9 A-54.9 None.. Ce(NO:)1 4X 85 8-9 A-59.4 d0....Ce(N0a)2 5X 85 8-9 A59.0 -d0.... Ce(NOs)z 6X 85 8-9 A-60.1 -do-..-..

TABLE XXV.--HARDNESS VARIATION WITH NUMBER OF COBALT OXIDE IMPREGNATIONSUSING COORS AP 94-12 ALUMINA REFRACTORY BASE MATERIAL No. HsPO4 salt;impregimpregnation, Mohs Rockwell Sample No. Oxide formed Saltimpregnation nations percent hardness hardness Cracks Remarks a-B C00000103), 85 9-10 A-71.5 None.- 4-B C00 C0(NO3)2 as 9-10 1 :73.0 None.-I-T C00 00(N03): 5X 85 9-10 A-74.5 None..

TABLE XXVL-HARDNESS VARIATION WITH NUMBER OF TUNGSTIC OXIDEIMPREGNATIONB USING COORS AP-Qi-IZ-ALUMINA REFRACTORY BASE MATERIAL No.H3130;

salt impregimpregnation, Mohs Rockwell Sample No. Oxide formed Saltunpregnatron nations percent hardness hardness Cracks Remarks HiSlWitOio6X 85 H4SlW1eO4o "7X "85 '9-l0"A-75.0

TABLE XXVIL-HARDNESS VARIATION WITH NUMBER OF FERRIC CHROMITEIMPREGNA'IIONS USING COORS AP-94I2 ALUMINA REFRACTORY BASE MATERIAL saltimpregimpregnation, Mohs Rockwell Sample No. Oxide formedSaltimpregnationnations percent hardness hardness Cracks Remarks 4-AFOzOaCXsOa (1)FeCl3+(1)Cr0a as (5-7 A-72 None--- 1-A.. Feeoaolgoa(1)F6Cls+(1)0!03 3X 85 9-10 A-75 d0 2-A- Fezogclzoa (1)Fe0l;+(1)0r0s 4X85 9-10 A-77 --do.. 3-A nezoaonoq (1)FeCl +(1)Cr0 5X 85 9-10 A-82 o Azirconia base material has been used for tests shown as Tables XXVIIIand XXIX. These are for a coarse grain, calcia stabilized, 95% zirconiaunderfired refractory material with chromic oxide and zirconium oxideimpregnations as shown.

A series of multiple phosphoric acid treatments of the Coors AP-94,AHP-99 and AP-85 alumina base material has been investigated. Theresults are shown in Tables XXX, XXXI and XXXII. For the most part,these tests TABLE XXVII[.--HARDNESS VARIATION WITH NUMBER OF CHROMICOXIDE IMPREGNATIONS USING DU-CO, CALCIA STABILIZED, 95% ZIRCONIA BASEMATERIAL No. HsPO4 salt impregimpregnation, Mohs Rockwell Sample No.Oxide formed Saltimpregnation nations percent hardness hardness CracksRemarks CrO 3X 85 6-7 A69.5 None.... CrO; 5 85 6-7 A-78.5 '..--do CrO;7X 85 6-7 A-77 ...do N None.... 85 8-9 A-54 ..-do

TABLE XXIX.HARDNESS VARIATION WITH NUMBER OF ZIRCONIUM OXIDE IMPREGNATIONS USING DU-CO, CALCIA STABILIZED, 95% ZIRCONIA BASE MATERIAL No.H 1 0; 7 salt impregimpregnation, Mohs Rockwell Sample No. Oxide formedSalt impregnation nations percent hardness hardness Cracks Remarks 23-2ZrO ZrO Oh 3X 85 6-7 A-65 None... 24- ZrO ZrO 01g 5X 85 d 25-2 ZrOr ZrOC12 7X 85 26-Z Nona None Nnnn 85 show that one phosphoric acid treatmentis equal to, or better than, more than one treatment.

TABLE XXXL-MULTIPLE ACID IMPREGNATIONS USING COORS AP-94-I2 ALUMINAREFRACTORY BASE MATERIAL Number HaPO4 Number Salt salt impregacid Mohsimpregimpregnation, impreghard- Rockwell Sample number nation nationspercent nations ness hardness Cracks Remarks 85 1X 8-9 A-68.7 None.....85 2X 8-9 A-67.8 -.--do..-.- 85 3X 6-7 A-67.7 .do 425/5 1X 4-5 A-64.8Yes..... Fractured.- 42% 2X 6-7 A-58.7 Yes..." Do. 42% 3X 6-7 A-58.5None.- Do.

TABLE XXXII.-MULTIPLE ACID IMPREGNATIONS USING COORS AP85-I1 ALUMINAREFRACTORY BASE MATERIAL Number H PO4 Number Salt salt impregacid Mohsimpregimpregnation, impreghard- Rockwell Sample number nation nationspercent nations ness hardness Cracks Remarks 85 1X A-61.2 Yes..... 85 2X.5 es Fractured. 85 3X None.... 42% 1X A-53.7 --d0.. 42 5 2XFractured..- Yes Do. 42% 3X 7. Yes-..--

TABLE XXXII.-MULTIPLE ACID IMPREGNATIONS USING COORS AHP-99 ALUMINAREFRACTORY BASE MATERIAL 3,734,767 I 24 Table XXXIII shows the same typeof multiple acid 'now been found that this marked increase in hardnessoctreatment test, except that the Coors (AP-94) material curs with atleast two single oxidestchromic oxide and has been first impregnatedwith three chromic acid apcobalt oxide, and at least two complex oxides;magnesium plications prior to the final acid treatments. Again, onechromite and iron chromite, when used as impregnants acid treatmentappears to be optimum. for one or more of the porous alumina. basematerials.

TABLE XXXIII.MULTIPLE ACID IMP RE GNATION TEST USIN G COO RS AP-94-I2ALUMINA REFRACTORY BASE MATERIAL WITH CHROMIC OXIDE PRE-TREATMENT NumberH3PO4 Number Salt salt impregacid Mohs 'impregimpregnation, impreghard-Rockwell Sample number nation nations percent nations ness hardnessCracks Remarks CrOa 3X 85 1X 9-10 A82.5 N0ne 01-0 3X 85 2X 9-10 A-SLOCrO 3X 42% 1X 9-10 A78.l CrO; 3X 42% 2X 9-10 A-SLO CrO; 3X 42% 3X 9-10A81.0

Tables XXXIV and XXXV show the eifect of varying A fifth impregnant,silico-tungsten acid, has also been the phosphoric acid concentration.'In the previous tests, found to react in a similar manner.

the acid strength has been either 85% or 42 /2% H PO Tables XXXVI andXXXVII respectively show the In these two tests 95%, 90% and 75%phosphoric acid hardness measurements obtained with AP-95-Il and arealso compared with the standard 85% strength treat- AHP-99 alumina basematerials with multiple chromic ment. Table XXXIV covers the AP-94'basematerial 'oxide impregnations only (no final acid treatment);'Table andTable XXXV the AHP-99 material. XXXVIII covers the same two baserefractory materials TABLE XXXIV.-EFFECT ON HARDNESS OF VARYING ACIDCONCENTRATION USING COORS AP94-I2 ALUMINA REFRACTORY BASE MATERIALNumber. H PO4 Number salt Salt impregacid Mohs impregimpregnation,impreghard- Rockwell Sample number nation nations percent nations nesshardness Cracks Remarks 95' 1X 5-6 A63.0 None 85 1X 6-7 A-65.0 d 1X 6-7A-59.5 42 /5 1X 4-5 A64.8 95 1X '9l0 A83.0 1X 9-10 A80.5 76 1X 8-9 A82.042 /5 1X 9-10 A-SLO 85 1X 940 A8l.5

TABLE XXXV.EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORSAHP-UJ ALUMINA REFRACTORY BASE MATERIAL Number H PO4 Number salt (1 Saltimpregaci Mohs lmpregimpregnation, impreghard! Rockwell Sample numbernation nations percent nations ness hardness Cracks. Remarks 1X 4-5A46.0 85 1X 6-7 A-56.0 75 1X 6-7 A-46.0 42% 1X 4-5 A3l.7 95 1X 5-6 A70.085 1X 45--A74.0 75 1X 4-5 A71.5

When conducting impregnation tests with various metal 7 with multiplemagnesium chromite impregnations only oxides, it was found that a markedincrease in the Mohs (30 and able X V Shows the Same CPOTS T vb d h AP 95 alumina matenal, but using multiple ferric chromite 1mbarduc s mf l f?f f m 4 pregnations. Table XXXIXA shows the Coors AP-94- even before thefinal phosphorlc acid treatment. It has 12 material with multipletungstic oxide impregnations.

TABLE xxxvt' almim'ss'umtiitatmnismoa l /IIJLTIPLE CrO IMPREGNA I i vr Tr ro ri T gr r g ACID TREATMENT USING oooas AP-M-IZ ALUQMINA anrnac o ye H Salt No. 11 1304 Mohs Base nnprcgsalt impreghard- Rockwell SampleNo. material nation nnpreg. nation ncss hardness Cracks Remarks 0-1AP-94-I2 CrOa 1X A-43.0 AP-Qql-IZ CrOa 2X A62.2 AP-M-IZ CrOa 3X A74.0AP-Ql-IZ CrOa 4X A-82.0 AP-94-I2 C1203 5X A84.0 AP-Q l-IZ 0x03 7X A-84.0AP-Q l-I2 CrOs 9X A84.5

7 Q 10 v.11 7 A-86.0

TABLE XXXVIL-HARDNESS MEASUREMENTS FOR MULTIPLE CrzOa IMPREGNATIONSWITHOUT FINAL ACID TREATMENT USING COORS AHP-99 ALUMINA REFRACTORY BASEMATE RIAL Moh's hard- Rockwell ness hardness Cracks Remarks 3-4 A-l5. 26-7 A-54. 7 89 A-69. 0 9-10 A-75. 0 9-10 A-78. 0 9-10 A-79. 5

TABLE XXXVIII.HARDNESS MEASUREMENTS FOR MULTIPLE MAGNESIUM CHROMITE IMPRE GNATIONS WITHOUT FINAL ACID TREATMENT H 1 0!- impreg- Mohs hard-Rockwell ness hardness Cracks Remarks Salt N0.

Base impreg salt Sample No. material nation impreg. nation MgCrO4 1XMgCrO4 3X MgCrO4 5X MgCrO4 1X MgCrO4 3X MgCrO4 5X TABLE XXX IIX.HARDNESS MEASUREMENTS FOR MULTIPLE IMPREGNATIONS WITHOUT FINAL ACIDREATMENT USING COORS AP-94-Il ALUMINA REFRACTORY BASE MATERIAL N0. saltHsPO4 impregimpreg- Mohs Rockwell Sample No. Oxide formed Saltimpregnation nations nation hardness hardness Cracks Remarks 4-AF6203Cl203 (1)FeCl3+(1)Cr03 1 None. 5A F82O3C1'2O3 (1)FeCl3+(1)Cr 3 3Xdo 0-A FezOsCHQs (1)FeCla+(l)CrOz. 5 .do

TABLE XXXIXA.HARDNESS MEASUREMENTSHFOR MULTIPLE TUNGSTIC OXIDEIMPREGNATIONS' WITHOUT FINAL ACID TREATMENT USING COORS AP-04-I2 ALUMINAREFRACTORY BASE MATERIAL Number Sample Base Salt irnsalt HQPO; im- MohsRockwell number material pregnation impreg. pregnation hardness hardnessCracks Remarks Compressive strength tests have been conducted forseveral treated refractory ceramics using the ASTM tentative standard,Method C528-637.

The date presented in Tables XL, XLI, XLII and XLIH TABLE XL.COMPRESSIVESTREN GTMEASUH REMENTS FOR COORS AP-94I1 ALUMINA REFACTORY BASE MATERIALUSING SINGLE ACID TREATMENT ONLY H PO4 Com- No. salt impregpressive .7;Salt imimpregnation, Sample Area strength, Sample No pregnation nationspercent diameter (in lbi psi. Remarks Average V 72,500

TABLE XLI.-COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-I2 ALUMINAREFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY No. saltimpregpressive Salt imimpregnation, Sample Area strength,

Sample N0." pregnation nations percent diameter (in?) lbf p.s.l.-Remarks 85 022 .303 26 SK 87,000 85 623 304 21 BK 71,800 85 625 .306 257K 83,800 85 621 302 29 OK 94, 000 85 .024 305 22 OK 72,300

Average 81, 800

TABLE XLII.COMPRESSIVE STREN GTH MEASUREMENTS FOR COO RS AP-85-I1ALUMINAREFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY No. saltimpregpressive Salt imimpregnation, Sample Area strength Sample No.pregnation nations percent diameter (in lbi p.s.i. Remarks 85 025 30017.8K 68, 300 85 025 306 20.0K 65, 500 85 .625 306 126K 41, 000 85 624305 12.7K 41, 600 85 023 301 1805K 02, 300

Average 53, 740

TABLE XLIII.COMPRESSIVE STRENGTH ALUMINA REFRACTORY BASE MATERIALMEASUREMENTS FOR COORS AP-QJ-Lii USING SINGLE ACID TREATMENT ONLY H3PO4Com- No. salt impregpressive Salt im: impregnation, Sample Areastrength,

Sample No. pregnation nations percent diameter (in?) 1151 p.s.i. Remarks85 .625 .300 230K 77,400 85 624 .305 21.7K 71,000 85 G25 305 21.6K 70,000

Average 73, 100

Tables XLIV, XLV and XLVI cover Coors AHP-99 base material with threeimpregnations of chromic oxide, magnesium chromite and zirconium oxide,respectively. A final, single acid treatment was also used in each case.

TABLE XLIV.COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-QE) ALUMINAREFRACTORY BASE MATERIAL USING CHROMIC OXIDE IMPRE GNATIONS PLUS SINGLEACID TREATMENT N0. salt impreg- Salt imimprcgnation,

Sample No. pregnation nation percent Com- pressive Sample Area strength,diameter (in?) Jf p.s.i. Remarks TABLE XLV.-COMPRESSIVE STRENGTHMEASUREMENTS FOR COORS AIIP-90 ALUMINA REFRACTORY BASE MATERIAL USINGMAGNESIUM CHROMITE IMPREGNATIONS PLUS SINGLE ACID TREATMENT IIgPOl Com-NO. salt impregpressive Salt imimpregnation, Sample Area strength,Sample No. pregnation nation percent diameter (in?) L] psi. Remarks N-2MgCrO4 3X 85 .250 .0402 4,175 83,500 N-3 MgCiOr 3X 85 250 .0402 3,57571,500

Average 77, 550

TABLE XLVI.COMPRESSIVE STREN GTH MEASUREMENTS FOR COORS AHP-00 ALUMINAREFRACTORY BASE MATERIAL USING ZIRCONIUM OXIDE IMPRE GNATIONS PLUSSINGLE ACID TREATMENT Coni- II3104 N0. salt impregpressi ve Saltimimpreg nation, Sample Area strength, Sample No. pregnation naticnpercent diameter (in?) p.s.i. Remarks N-5 ZlOClz 3X 85 .240 .040 2, 37547, 500 N-fi Zl'OClz 3X 85 .250 .040 1,800 36,050

Average 41, 775

TABLE XLVII.COI\IP RESSIYE STREN GTH MEASUREMENTS FOR COORS AP0-111ALUMINA REFRACTORY BASE MATERIAL USING CI'IROMIC OXIDE IMPREGNATIONSH3PO4 Com- No. salt impregpressive Salt imimpregnation, Sample Areastrength, Sample No. pregnation nation percent diameter (in?) p.s.i.Remarks C-5 CrOz. 3X 85 .251 .049 0,100 123,730 (-0 CrOt 3X 85 .251 .0490,600 133,333

' Averagenzh; 128,532"

Modulus of Rupture tests have been conducted using chromic oxideimpregnations and with chromic acid plus the procedure of ASTM MethodC36956 with the eX- other oxide impregnations.

TABLE XLVIIL-MODULUS OF RUPTURE TEST DATA FOR COORS AP-94-12 (ISOSTATIC)ALUMINA REFRACTORY BASE MATERIAL 11 104 impreg- Salt im- N0. saltnation, Support Modulus of Samplenumber pregnations impreg. percentDiameter distance Lbf. rupture Remarks TABLE XLVIIIA.MODULUS OF RUPTURETEST DATA FOR COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL HaPOi No.impreg- Support Sample salt nation, distance, Modulus number Saltimpregnations impreg. percent Diameter inches Lbf. of rupture Remarks 85260 1. 50 82 17, 900 3x 85 .258 1. 50 125 27, 900 3X 85 .258 1.50 11024, 500 6X 85 258 1. 50 84 18. 700 6x 85 260 1. 50 164 35,700 85 1.50148 33, 000 CrOa-I-ZrOClz -.{:1) 85 -257 1.50 128 28, 900or03+Ni(No.)2.-.- 85 1.50 110 24,000 16; C1'Oa+Ni(NO3)2... 85 V v 258 1.124 27, 600 17 CrO3+H4SiW15O10.--{ 85 258 1. 50 105 23,4001'9..."..--1-"5165556155..-. 85 1.50 so 17,800

ception that the sample size has been reduced. The ASTM Specific gravitydeterminations for a number of the po- Method calls for samples A" indiameter x 6" in length. rous refractory base materials, measured in thereceived The present ceramic samples have been prepared with condition,is presented in TableXLVIX.

TABLE XLVIX.SPECIFIC GRAVITY DETERMINATION FOR VARIOUS REFRACTORY BASEMATERIALS WITHOUT OXIDE OR AQID,TREATMENTS (ASRECEIVED CONDITION) Weightin Base Salt No. salt H3PO4 Volume air (dry) Length Diameter SpecificSample number material impreg. impreg. impreg. (60.) (gms.) (cm.) (cmgravity A99 AHP-9 None None 1. 684 3. 1. 471 1. 210 2. 10 AP-99 L3 1.674 3.95 1.474 1. 205 2. 36 1. 645 3. 94 1. 456 1. 200 2. 39 1. 678 4.15 1. 478 1. 205 2. 47 1. 696 4. 21 1. 494 1. 205 2. 48 E421 --d0-.do 1. 678 3. 1. 478 1. 204 2. 14

Isostatic.

v V v v H Specific gravity measurements for some of these samedimensions on the order of A in diameter x 2" in length. materials, butprocessed with a single phosphoric acid The sample size change was madebecause of the lack of treatment, is listed in Table L.

TABLE L.S1?ECIFIC 'GRAVITY'DETERMINATION FOR VARIOUS REFRACTORY BASEMATERIALS WITH SINGLE ACID TREATMENT ONLY Weight H3PO4 in air Base SaltN0. salt impreg., Volume (dry) Length Diameter Specific 1 11}? ne th t ral. im t9 mP Ps-. P r nt. -l ta -X 77 gravity A99 AHP-QQ None 85 1.71 4.31 1.494 1.210 2.52 AP-99-L3 85 1.678 4. 63 1 474 1 206 2.75 AP-85-ll 851.632 4. 49 1. 466 1 194 2.75 AP-94-I1 85 1.671 4.74 1 475 1 204 2.83AP-94-I2 85 1.602 4. s3 1 404 1 204 2.85 AP-94-12 85 1.675 4. a2 1 47s 1203 2.58

I Isostatic.

curing ovens long enough to conveniently handle the 6" Table LI showsspecific gravity measurements for piece, Coors AP-99L3 alumina basematerial with 1 through Table XLVIII lists the modulus of rupture testresults 11 chromic oxide impregnations. This table shows that a for theCoors AP-94I2 base material with multiple maximum density was obtainedWith six chromic oxide (zero, three and six) chromic oxide impregnationsTable impregnations.

TABLE LI.SPECIFIC GRAVITY DETERMINATIONS FOR COORS AP09L3 ALUMINAREFRACTORY BASE MATERIAL WITH MULTIPLE CI-IROMIC OXIDE IMIREGNATIONSWeight sPO4 in air Base Salt N0. salt impreg., Volume (dry) LengthDiameter Specific Sample number material impreg. inipreg. percent (00.)(gins) (cm.) (em.) gravity AP-99-L3 0103 1X None 1.337 3. 704 1. 555 2.77

AP-99-L3 CrOa 3X 1. 340 4. 23 710 1. 555 3. 09

AI99L3 ClOs 5X 85 1. 368 4. 74 714 1. 563 3. 46

AP-99-L3 CrOa 7X 85 1. 337 4. 704 1. 555 3. 70

AP-99-L3 01'03 9X 85 1. 301 5. 30 .726 1.563 3.81

6 AP99L3 CrOa 11X 85 1.334 5.07 696 1.564 3. 80

XLVIIIA lists the modulus of rupture tests for the Coors To determinethe effective porosity of these ceramic AP-99-L3 base material withmultiple (three and six) materials, water absorption tests were made.The porosity percentage was calculated by determining the weight of theabsorbed water in grams divided by the volume of the sample in cubiccentimeters. This type of measurement gives the effective porosity onlysince there may be completely entrapped pores or pores too small toadmit water.

Table LII shows the eifective porosity measurements made for a number ofthe porous, underfired refractory base materials prior to any treatmentof any kind. These materials show porosity variations ranging from about30% to about 50% for the types tested.

occurred after ten cycles in either environment. Mohs hardnessmeasurements also remained unchanged from the pre-test condition.

All the ceramic type materials produced according to the presentinvention have been repeatedly cycled between ambient temperature and2000 F. This includes Coors AHP99, AP-94, AP-85 to AP-99, basic aluminamateral with 01- 0 MgCr O Zr0 and many other multiple oxideimpregnations, as well as several similar combinations with theberyllia, zirconia and magnesia base TABLE LIL-EFFECTIVE POROSITYDETERMINATIONS FOR VARIOUS REFRACTORY BASE MATERIALS WITHOUT OXIDE ORACID TREATMENT [As received condition] ase mpreglmpregsoa e in r 2 S. 0ume orosity Sample number material nation number nation H20 (gms.)(gms.) absorbed (ce.) pereent l Isostatic.

Table LIII shows the same type data as above except that the porous basematerials have been given a single phosphoric acid treatment only.

materials. It has also been found that ceramic parts produced by thisinvention can be cooled very rapidly after heating to high temperatures.For example, a thin cross TABLE MIL-EFFECTIVE POROSITY DETERMINATIONSFOR VARIOUS REFRACTORY BASE MATERIALS WITH SINGLE ACID TREATMENT ONLY BSalt lnlliaPOi k (llNt. i1; H o( V 1 Eflective ase impregpregsoa e inair ry z s. o ume orosity Sample number material nation Number nation H(gms (gms.) abso i h ed (00.) percent 1 Isostatic.

Table LIV Presents data Obtained y using 1 through section piece can beremoved from a 2000 F. oven and 11 chromic oxide impregnations followedby the single acid treatment. In this test, Coors AP-99-L3 base materialwas used. As in the case of the specific gravity measurements, minimumporosity occurs at about 9-11 impregnations.

placed directly on an aluminum cooling plate without cracking.

Thin plates of Coors AHP99 base material with single acid treatment havebeen exposed continuously to 1000 F. for 6 /2 days. No fracturing orcracking could be TABLE LlV.-EFFECTIVE POROSIIY DETERMINATIONS FOR COORSAP99L3 ALUMINA REFRACTORY BASE MATERIAL WITH MULTIPLE CHROMIC OXIDEIMPREGNATIONS Wt. soaked Wt. in air H2O Efieetlvo Base Salt 1111* H P04imin H O (dry) (gms) Volume porosity,

Sample number matenal pregnation Number pregnation (gms) (gms.) absorbed(00.) percent 1 AP-99-L3 CrOs 3. 95 3. 70 25 1. 337 18.

AP-99-L3 CrOa 4. 52 4. 23 29 1. 349 21. 5

AP-99-L3 CrOa 4. 95 4. 78 21 1. 368 15. 3

AP-99-L3 CrO; 5. 10 4. 95 15 1. 337 11. 2

AP-99-L3 CrOa 6. 32 5. 30 02 1. 391 1. 43

6 AP-99-L3 CrOi 5. 08 5. 07 01 1. 334 0. 74

Samples of AHP99 alumina, with single acid treatment only, have beenfabricated in the form of thin discs measuring /1" x 3". They were thenheated to 1000 F. and water quenched, reheated to 1000 F. and againquenched for a total of ten cycles. No visible signs of cracking orchecking were observed.

The same type test has been performed with similarly prepared samplesusing liquid nitrogen as the quenching media. While liquid nitrogen doesnot produce as severe a thermal shock as does a good conductor such aswater, it does, however, provide a much wider temperature excursion. Thesamples were left immersed until gas formation ceased and it isestimated that a temperature of about 300 F. had been reached. Again, nocracks or fatiguing were noticed after ten cycles.

These two thermal shock cyclings (1000 F. and liquid nitrogen) wererepeated using AP-94-I1 alumina base material. These samples wereprepared, however, with three, five and seven chromic oxideimpregnation's prior to the final phosphoric acid treatment. In thiscase, the samples measured approximately A3" in thickness by indiameter. Again, no cracking or structural failure detected and thepreand post-exposure hardness measurements were identical.

Additional samples were prepared using Coors AHP99 and AP-94-l2 basematerial with three magnesium chromite and five chromic oxideimpregnations respectively. In each type sample, a final acid treatmentwas used following the oxide impregnation. These samples were exposed to1000 F. for 60 hours followed by 8 hours at 2000 F. Again, no structuralor hardness changes could be observed.

Sample ceramic parts (approximately 4;" thick x in diameter) using AHP99base material with a single acid treatment have also been immersed inliquid nitrogen for 16 hours and then removed and returned to roomtemperature. No change in hardness was observed and no evidence ofcracking or fractures could be found.

Tests have been conducted with machined rods and discs of ceramicmaterials produced by the instant process to determine what changesoccur in dimension between the pie-hardened and the treated and hardenedcondition. The accuracy of these measurements is considered to be1-.0001 inch.

33 Table LV covers AP-99-L3, AP-SS-Il and AP-94-I2 porous aluminamachined pieces before and after a single acid treatment. These partswere cured at a final temperature of 1800 F.

3.4 It will be noted that in each X-ray diffraction study of an aluminumoxide ceramic sample which has been subjected to a phosphoric acidtreatment according to the present invention, there appears a line whichhas been TABLE LV.-DIMENSIONAL CHANGE TESTS FOR HARDENED VS.PRE-HARDENED CERAMIC MATERIAL [Mare temp. 1,800 E, 1 hr.]

H 1 Pre-hardened I Salt impregdimensions Hardened dimensions Percentchange Sample Base impregnation,

number material nation Number percent Length Diameter Length DiameterLength Diameter 85 4. 957 0. 3553 4. 955 0. 3652 O. 040 0. 027 85 0.7001 0. 3781 0. 7001 0. 3779 0 0. 058 85 U. 9467 0. 8536 0. 9457 0. 85320. 105 O. 045 85 0. 8521 1. 0940 0. 8521 1. 0940 0 0 85 0. 1954 0. 75600. 1954 0. 7555 0 --0. 066 85 0. 8971 0. 3040 0. 8963 0. 3037 0. 089 O.096

Norn.-Pre-hardened dimensions were read from the machined base materialprior to any chemical treatment. Hardened dimensions were read afterchemically treating part and curing to 1,800 F. for 1 hour.

Table LVI shows dimensional change readings for AP-99L3 and AP-94-12materials treated with multiple oxide impregnations followed by a finalsingle acid treatment and cured at a final temperature of 1800 F.Percentage values, as above, reflect change in dimension between thoseof the original machined basic porous structure and those obtained afterthe part has been chemically treated and hardened. As can be seen, thedimensional changes are exceedingly small.

labeled X as there is no existing information in the X-ray indexes of aline having been previously observed at this position. As shown in theTable LVII, the untreated AHP99 and AP-94 alumina samples A and B do notdisplay the X line, while samples C and D and the others treated withphosphoric acid according to this invention do provide the X line. The Xline occurs at a d spacing of approximately 4.12 A. The nearest compoundis that of AlPO aluminum ortho phosphate having the most TABLELVL-DIMENSIONAL CHANGE TESTS FOR HARDENED VS. FEE-HARDENED CERAMICMATERIAL [Max. temp. 2,300 F., 2 hrs.]

HzPOi Pre-hardened Salt impregdimensions Hardened dimensions Percentchange Sample Base impregnation, number material nation Number percentLength Diameter Length Diameter Length Diameter D70 AP99 L3 CrOa 3X85 1. 9765 0. 2570 1.9765 0.2570 0 0 D71- AP-99-L3 (3103 6X 85 1. 97600.2595 1. 9765 0. 2595 +0. 025 0 D72- AP-99-L3 ZrO Ola 5X 85 1. 9760 0.2579 1. 9705 0. 2579 +0. 025 0 D73. AP-94- CrOa 3X 85 1. 9824 0.2590 1.9815 0. 2590 0. 045 0 D74. AP-94-I2 l grOa 2X 85 1. 9916 0.2592 1.99100.2592 -0.030 0 I03 X D75 AP-94-I2 C12 2X }85 1. 9805 0. 2681 1. 9800 0.2681 0. 020 0 n Isostatic.

Norn.-Pre-hardened dimensions were read from the machined base materialprior to any chemical treatment. Hardened dimensions were read afterchemically treating part and curing to 1,800 IE Various of the treatedceramic materials have been subjected to anumber of standard solventsand reagents. Little or no efiect'has been observed. Immersion tests fortreated ceramics utiliiing the single acid treatment only and forceramic types incorporating various oxide impregnations, both with andwithout the'final acid treatment, have been made in acetone,trichlorethylene, hydrochloric acid, sodium hydroxide, sea water, ferricchloride and concentrated sulfuric acid with no observable effect oneither the hardness or physical appearance.

X-ray diffraction analysis of the structure of several types of treatedceramic materials has been conducted using a Norelco difiractometermanufactured by North AmericanPhillips, Inc. Th'e'results are brieflysummarized in the following Table LVII. Accuracy of measurements can beconsidered to be at least 0.1%.

TABLE LVII.-X-RAY DIFFRACTION CRYSTAL STRUCTURE IDENTIFICATION SampleBase Salt H PO4 X-ray diffraction Number material impreg. N0. impreg.identification None None A120;

intense line with a d spacing of 4.077 angstroms, relative intensity inthe 1-11 planes; next most intense line d spacing 2,506 angstroms,relative intensity 20, 2-2-0 planes; next most intense line d spacing 2.867 angstroms, relative intensity 10, '1-1-2 planes; next line d spacing3.162 angstroms, relative intensity 10, 0*21 and 201 planes. There are anumber of lesser intense lines. It is important to note, however, thatnone of the lines with d spacing of 4.077 A.; 2.506 A.; 2.867 A.; 3.162A. or any of the remaining lines appear on the X-ray diifraction chartof the aluminum oxide ceramic materials which have been treated withphosphoric acid according to the pressent invention. It is assumed thatthe phosphoric acid treatment results in or produces a new compound orat best a new crystalline structure which accounts for the improved andunique properties of the treated aluminum oxide materials. The source ofinformation for the X-ray data on aluminum ortho phosphate is theNational Bureau of Standards Circular No. 539, Oct. 4, 1960.

Samples of ceramic material formed using Coors AP- 99f-L3 alumina baserefractory material with single acid treatment only (no oxideimpregnation) have been subjected to various nuclear radiationenvironment.

One such test consisted of exposing small coil forms made of thematerial to a transient nuclear environment in a fast burst reactor. Inthis case, the small pieces A" diameter x /8 length) were exposed to aneutron flux rate of 2.8x 10 n./cm. -sec. with associated gammas of 6 10rads/sec. The total dose per burst was -2.2

10 n./cm. (fast neutron), 1.8x 10 n./cm. (thermal neutrons) and 5X 10rads. No noticeable eflect in the ceramic material could be detected.

Another test was conducted in which small samples of the same typeceramic were irradiated for a period of time long enough to accumulate atotal exposure of approximately (z mev.). Even with this very highexposure, no physical change in the ceramic part could be detected.

Parts to be fabricated using the method and materials of this inventionare first machined to the correct dimensions from the relatively soft,partially sintered, porous refractory base material.

In this original, untreated condition, the material will normally have aMohs hardness somewhere between 1 to 3 and preferably between 2-3 (suchas the Coors AHP-99 and AP-94 alumina).

This hardness range allows machining using ordinary high speed steel orcarbide tool bits, drills, cutters, saws, etc. While carbide tooling isrecommended for quantity production to reduce tool wear, high speed toolsteel will also hold up quite Well providing cutting speeds are low toprevent heat buildup at point of contact.

Very fine and intrincate parts can be machined and processed from thismaterial. Thin walled parts, such as coil bobbins, can be made withsections as thin as .010" with little difficulty. Also, providing slowspeeds are used to prevent heating, holes as small as have been drilledto an inch or so in depth.

Recommended lathe turning speeds for small parts (l.4"2" dia.) are about250 r.p.m. and drilling should ordinarily be done at speeds of less than150 r.p.m. Band saw cutting should be at 10 ft./min. or less. Finishedparts may also be easily sanded by hand using conventional wet or dritype silicon carbide paper with grit size ranging from 100 to 600,depending on the final finish desired.

Since the part will become extremely hard following the chemicaltreatment and hardening process, the dimensions and surface finishdesired in the final cured state should be completed during the initialmachining operation. It is possible to provide final polishingoperations after not more than three oxide inpregnations using siliconcarbide paper. After this point, it will usually be necessary to resortto diamond machining since the hardness of most of the hardened ceramicmaterials will usually exceed that of silicon carbide.

In order to fabricate a hardened ceramic part according to thisinvention, the piece, machined from the soft, base refractory material,must next be chemically treated and cured.

The chemical treatment method will normally consist of one of thefollowing: (1) impregnation in phosphoric acid only; (2) One or moreoxide impregnations followed by a single phosphoric acid treatment; (3)One or more oxide impregnations without final acid treatment. The choiceof impregnation method will, of course, depend on the final physical,chemical and electrical properties desired, as well as the economicfactors involved.

Following each chemical impregnation, the part is elevated intemperature to remove the water (including water 36 of crystallization)and to convert the salt, or acid solution to an inert crystallinestructure. A typical impregnation and curing cycle is shown in TableLVHI.

TABLE LVHI.-CURING AND HARDENING CYCLE FOR UNDERFIRED REFRACTORYCERAMICS The above applies to any part having its thinnest section notexceeding For thicker pieces, longer curing cycles (steps 3 and 6) andimmersion times (steps 2 and 5) are required. Steps 2 and 3 may berepeated for desired number of salt impregnations, depending onmechanical strength properties desired. Where only acid treatment isdesired, steps 2, 3 and 4 can be omitted. In like manner, if only anoxide treatment is to be used, steps 5 and 6 can be omitted.

Many of the refractory ceramic materials of this invention have beenfound to exhibit excellent characteristics for bearing and sealapplications. Even the simple acid treated refractory base materialsexhibit a noticeably low coefficient of friction characteristic,suggesting possible bearing use.

Static and sliding coefficient of friction data has been measured forseveral refractory ceramic materials produced in accordance with thepresent invention.

Table LIX lists static coefficients determined by sliding various oxideimpregnated specimens on a chromic oxide impregnated slide. The slideand most of the oxide impegnated sliders were also given a finalphosphoric acid treatment. As can be seen from the data presented inTable LIX, the lowest coeflicient is provided by the like materials. Theone sample, given four chromic oxide impregnations followed by onezirconium oxide impregnation (plus final acid treatment), produced thehighest friction coefficient when sliding against the chromic oxidetreated slide.

Table LIX shows that the lowest friction coefiicients are generallyobtained by sliding identical ceramic materials against each otherrather than unlike materials.

TABLE LIX.COEFFICIENT OF STATIC FRICTION MEASUREMENTS, RUN DRY SliderSlide HaPO4 H3P01 Salt impreg- Salt impreg- Friction impreg- Numnation,Base impreg- Numnation, Load cqetli- Base material nation ber percentmaterial nation ber percent (lbs.) Lb.f clent AP-94-12 CrO 5X None 111-94-12 CrO 4X 62.38 8.2 .131 AP 9412 CrOs 5X 85 AP-94-12 CrOa 4X 8562.38 11.4 .183 AP-94-12 ZrOCOz.- 5X 85 AP94-12 CrO; 4X 85 62.38 9.6.154. AP94-12 MgCIO4 5X None AP-94-12 CrO; 4X 85 62.38 9.8 .157 AP-94-12Ni(N0a)2. 5X 85 111 -94-12 CrO 4X 85 62.38 8.8 .141 AP-94-12 C0(N0a)z 5X85 AP-94-12 CrOa 4X 85 62.38 8.3 .133 AP-94-12 SnCl 5X 85 AP-94-12 CrO4X 85 62.38 9.3 .149 AP-9 1-12 %oge- 85 AP-94-12 CrO 4X 86 62.38 10.7.172

l 3 4X AP-94-12 plus 85 111 -94-12 CrO; 4X 85 62. 38 11.3 .181

ZrOC12 1X N ore-Contact area of slider=.6 in

Table LXI lists coefficients of friction for some com- ....the shoe. isattached. The wheel is directly driven by mon materials-and'is'includedfor comparison purposes. W 7 means 'of an electric motor. The slow drivespeed has been used because wear rates are generally more severe at slowspeeds than at high speeds since more surface-tosnrface contact canoccur through the lubricating film.

TABLE LXL-fCOEFFICIENT. OF STAZ'IIC dgID SLIDING Since the shoe has aflat contacting surface, the live Materials dry dry contact pressurebetween shoe and wheel is extremely Glass on glass M4 0 4 high at thebeginning of the test. As would be expected, Hard steel on hard steel--0.78 0,42 therefore, the highest wear 15 experienced at the start of521% 8g gi f f 3 :55 the test with the wear rate diminishing with time(as the Brass on mild steel; 0. 51 0.44 shoe wears, the p.s.i. loadingdecreases). While this type gg ggxzg ffii f?" 8:52 arrangement is unlikeany actual bearing design, it does Teflon on steel: 0.04 0. 04 allow aconvenient and rapid means of comparing wear Tungsten carbide ontungsten carbide" 0. 2 rates. Tungsten carbide on steel 0.5

Table LXII lists the types of treated refractory ceramic materialstested using the rub-shoe arrangement. For

the most part, the variations consist in the oxide impreg- Wear ratetest data was obtained with a variety of nation employed, which has beenfound to be a significant treated refractory ceramics using a singlerub-shoe type factor in the wear properties. Unless otherwise specified,

test. Both conventional and non-conventional lubricants the shoe widthhas been standardized at 0.25" with a have been used in these wear ratetests, including #10 wheel diameter of 1.10.

TABLE LXII.RUB-SHOE TEST PARTS No'rE.Above data from American Instituteof Physics Handbook,- 1957.

- Final Part Base 'Num- 2nd Numimpreg., Rockwell Mohs number material1st impreg. ber lmpreg. ber percent hardness Hardness Remarks SAE motoroil,-glycerine, #200 polyethylene glycol, G.E. Tables LXIII throughLXVII show comparison runs F-SO Versilube silicone lubricant, alcohol,gasoline, parfor various treated refractory ceramic materials using aaffin, aprizon high vacuum grease, tap water and sea variety oflubricants. Some comparisons have also been water. I made withconventional bearing materials such as a bear The rub-shoe testarrangement consists of a single shoe ing bronze shoe riding against amild steel wheel. Such riding against the periphery of a rotating-wheel.The comparisons, however, are not too meaningful since the wheel inthese tests have normally been operated at metal bearings are used onlyunder very lightly loaded either to 300 r.p.m. The contact pressurebetween the conditions with good lubricants or else galling occurs.

I shoe and wheel is variable and may be adjusted simply 45 The bettertreated refractory ceramic materials under these by changing Weights onthe end of 'a lever arm to which conditions show negligible wear.

- "IABLE LXIIL-RUB-SHOE WEAR-RATE COMPARISON TESTS Load 10 lbs., RunTime, 1 hr., Lubricant Alcohol, r.p.m. 300, Wheel Diameter 1.1, ShoeWidth .25, Base Material AP-94-12 Wear H 190 HaPOi Wear Wear CorrectedWear rate Wheel Salt impreg., Shoe Salt unpreg., depth length depthwidth (in/ft.) No. impreg. N0. percent No. impreg. No. percent (m.)(in.) (in.) (in.) 10 Remarks W-l OrO 5X None W1 CrO 5X None .000345 .240.00033 .030 5X 85 W-2 CIOs 5X 85 .00029 .235 .00027 .030 53 4X CrOa 4X85 W-3 plus 85 .00010 .250 .00010 .025 20 1X ZrOCli 1X 85 W-5 None 85.000885 .250 .00089 .060 175 5X 85 W-6 Zl'OClz 5X g 85 .00075 .250.00075 .000 147 5X None W-7 MgCr04 5X None .000485 .250 .00049 .045 965X- 85 W-8 Ni(N0z)2 5X 85 .000465 .250 .00047 .050 92 5X 85 W-Q 00(N03):5X 85 .00125 .250 .00103 .075 200 5X 85 W-lO SnOlz 5X 85 .00055 .250.00055 .050 107 8X 85 W 1 A CrO 8X 85 .00000 NM. .00000 N.M. 0

i TABLE Lxrv.-RUB-sH0E WEAR-RATE COMPARISON TESTS Load, 301bs., RunTime, 2 hrs., Lubricant Alcohol, r.p.m. 300, Wheel Diameter 1.1, ShoeWidth .25", Base Material AP9412 Wear H PO HQPOQ Wear Wear CorrectedWear rate Wheel Salt impreg., Shoe Salt impreg., depth length depthwidth (in/ft.) No. impreg. No. .percent No. impreg. No. percent (in.)(in.) (in) (in.) 10- Remarks 'W.1 CrO 5X None W1 CrOe 5X None .00050.235 .0004? .045 46 W-2 Gr03 5X 85 W-2 CrOa 5X 85 .00041 .220 .00036.035 35 CrOa 4X CrOa 4X w-a lus s5 w-a plus v 85 .000315 .220 .ooo2s.035 28 ZrOCl 1X ZrOClz 1X W-2 CrOe 5X 85 W9 00(N03)2 5X '1 85 .0093.245 .00091 .055 89 W-9 806N002 85 W2 CrOe 5X 85 .0071 .250 .00071 .060

l 3 W- plus W-2 ,CrO; 5X 85 .0026 .230 .00024 .030 24 ZrOCli 1X 0103 4XW2. OrO; 5X 85 W-3 plus 85 .0031 .200 .00025 .040 25 z o on 1x TABLELXIV-Contlnued Wear HQPO4 H PO Wear Wear Corrected Wear rate Wheel Saltlmpreg., Shoe Salt impreg., depth length depth width (in./tt.) No.lmpreg No. percent No. impreg. No. percent (in.) (in.) (in.) (in.) X10-Remarks CrOa 4X CIOs 4X Re-run alter w-s plus 85 we plus 85 .00001 .220.00021 .035 21 wheel well ZrO 01; 1X ZrOClz 1X polished. W1-A CrOa 8X 85W-l-A CrOz 8X 85 .000045 .215 .00004 .020 4 W-S Ni (N03): X 85 W8 Ni (N03): 5X 85 .000765 245 .00075 .065 74 TABLE LXV.--RUB-SHOE WEAR-RATECOMPARISON TESTS Load, lbs., Run Time, 1 hr., Lubricant H7O, r.p.m. 300,Wheel Diameter 1.1", Shoe Width .25, BaseMatcrial AP-94-12 Wear H IO4H3PO4 Wear Wear Corrected Wear rate Wheel Salt imprcg, Shoe Saltimpreg., depth length depth width (in/ft.) N0. iinprog. No. percent No.impreg. N0 percent (in.) (in.) (in.) (in.) X10' Remarks W1A CrOa, 8X 85W-l-A CrOa 8X 85 N.M. N.M N .M. N.M. N.M. High wear.

CrO; 4X CrOa 4X W-3 plus &5 W-3 plus 85 000135 190 000103 025 ZrO Cl2 1XZrOClz 1X W-2 CF03 5X 85 W-2 CrOa 5X 85 000145 245 000142 035 28 None 85W-5 None 85 N .M. N.M. N.M. N.M. N .M. D0.

ZrOClz 5X 85 W-6 ZrO Clz 5X 85 N.M. N.M. N.M. N.M. N.M. squeaks. MgCrOr5X None W-7 MgCrO4 5X None 00094 250 000940 070 177 Ni(NOa)z 5X 85 W-8Nl(NOa)2 5X 85 N. N.M. N.M. N.M. N.M. D0. Co(N03)2 5X 85 W-9 Co(NO3)2 5X85 N.M. N.M. N.M. N.M. N.M. D0. SnClz 5X 85 W-lO SnClz 5X 85 (D286 230000263 115 52 CrO; 6X W-2-A CrO; 5X 000055 225 000050 020 10 1 85% plusAlPO4.

TABLE LXVI.LUB RICANI COMPARISON RUNS USING w-s RUB-SHOE (NiO-SXIMPREGNATION) Bun Wear Wear Wear Wear Run Load time depth lengthCorrected width rate number Lubricant (lbs.) (hrs.) R.p.m. (in.) (in.)depth (in.) (in.) (in./lt.) Remarks 1 Alcohol a0 2 300 .000765 .245 .065gr 2 300 000405 250 000248 050 24 30 2 300 N.M. N.M. N.M. N.M. N.M. 30 2300 000005 175 010 5 Paraffin 30 2 300 TABLE LXVIL-LUBRIOANT COMPARISONRUNS USING W-3 RUB-SHOE (CrO -SX IMPREGNATION) Run Wear Wear CorrectedWear Wear Load time depth length depth width rate Run number Lubricant(lbs.) (hrs.) Rpm. (in.) (in.) (in.) (in.) (in./ft.) Remarks 1 TapWatch... 30 2 s00 N.M. N.M. N.M. N.M. 2 Alcohol 30 2 300 00001 220 03588 3--- #10 SAE oil--- 30 2 300 000005 235 .025 .40 4 Tap water. 10 1300 The treated refractory ceramic material has been found to performmost satisfactorily as a bearing when used against a like material. Thisis unlike metal bearings where different metals are invariably used toachieve low wear rates. The reason for this behavior is not fullyunderstood.

The Bearings and Seals branch of the Marine Engineering Laboratory ofthe U.S. Navy Department employs a single rub-shoe test for their seaWater lubricated materials. In this case, the shoe has a 1 width(usually made as a 1" cube) and rides on a 1%" wide x 2 diameter wheel.The r.p.m. is adjustable over a range of from 3 to 300. The standardloading is 4 lbs.

Similar tests were conducted using several of the single oxideimpregnated chemically treated and hardened ceramic materials. Wearrates were measured to be between 1.55 X 10- and 3.1 x 10- inches ofwear/ft. of travel with 1" contact length, 4 lb. load at point ofcontact, 60 r.p.m. Wheel speed, sea Water lubrication and 92 hoursrunning time. This is at least two orders of magnitude less wear thanwith the titanium carbide/carbon combination presently being used forsubmarine seals by the M.E.L. Multi-oxide impregnated materials provideeven lower Wear rates.

Life tests have been made on several bearing configurations. They havebeen lubricated with various oils and water. Two oil lubricated bearingshave a total running time to date of over 6615 hours at 1800 r.p.m.without any visible signs of wear. A radially loaded dual bearing hadone bearing running in #10 SAE motor oil and the other running under seawater operated at 3200 r.p.m. The load on these bearings totals 1.5pounds. These bearings have been operated continuously for over 5272hours with no sign of wear. It should be noted that a bearing to be usedwith or under water should be cured at a temperature which is at leastsufilciently high to drive all of the water of crystallization out ofthe ceramic and convert the structure thereof to a water-insolublestate. As indicated previously, this temperature is found to be at leastabout 600 F. to about 1000" F. for the aluminum oxide ceram1cs.

It will be appreciated that these bearings have marine applications in asubmersible system and would not require special seals, speciallubrication or added buoyancy problems. Silicone lubricated bearingswould be useful in low temperature applications and the bearings arealso useful in liquid metal lubricated systems.

From room temperature to 600 F., the coefl'iicent 0f the treatedrefractory ceramic materials has been found to remain extremely low. Theceramic materials exhibit a higher friction cocfiicient between about800 F. and 1200 F. Above this temperature, however, it again begins toslide more freely, attaining a reasonable low coefiicient as 2000 F.temperatures are approached. Since this behavior of increasing and thendecreasing friction with temperature is almost identical to thatreported for fully vitrified aluminum oxide ceramics, it is expectedthat the aluminum oxide base of the treated refractory ceramic is themajor contributing factor to the related elevated temperature behavior.

The fact that the treated refractory material can be fabricated with arelatively high degree of porosity suggests the possible use of solidlubricants. This can be accomplished by impregnating the porous ceramicwith a salt solution convertible to a solid lubricant, such as a salt of

